SOME NOTES ON FABRIC VARNISH
It is really strange that no one in England has yet invented a really satisfactory fabric varnish, for there would no doubt be a considerable market for a preparation that would render ordinary cotton material air proof, damp proof, and impervious to the rotting effect of the castor oil that habitually soaks those surfaces in the wake of the engine exhaust, that would reduce the skin friction of the fabric and have the effect of shrinking, and so tightening it when applied after the fabric is in position.
Quite noticeable was the difference in the condition of the fabric on the wings of Beaumont’s and Vedrines’ machines after their 1,000-mile arduous journey round Britain. On the wings of Beaumont’s monoplane the fabric had become stretched and baggy, so much so in fact that many would have deemed it inadvisable to have used the wings again before they had either been recovered or the fabric reapplied.
Although Bleriot uses undoubtedly one of the best of rubberised fabrics, this sagging can only be accounted for by the assertion that rubber, although excellent in some respects, is by no means the best proofing agent it is possible to use, as it is as susceptible, and probably more so, to extremes of atmospheric temperature and humidity as is the fabric itself.
Again, it is universally known that oil and grease have a deleterious effect on rubber, and one would have thought that for this reason, if for no other, constructors and others interested would have sought out a means of further protecting the fabric on those surfaces, to the rear of a machine, that are constantly receiving a shower of finely divided oil.
Vedrines’ wings were, on the other hand, in as good condition as the day they were made. The high-toned drum-like sound, when the fabric was snapped with the finger, indicated that all the adverse conditions of sun, wind and rain had not altered its character in the slightest. The tail planes too, although covered with a film of oil were, none the less, tightly stretched and by merely wiping them with a petrol-soaked rag all traces of castor oil could be effectively removed.
The varnish that is used to treat the Morane wings is colourless and transparent, and is applied after the fabric is stretched over the wing skeleton. Its application, in addition to shrinking the fabric, has the effect of embedding the rough weft and warp of the material, thus presenting a perfectly smooth surface, and consequently diminishing skin friction. The base of the varnish is singularly like celluloid as far as outward appearance is concerned, but it is hardly likely to be of this inflammable material.
It has occurred to the writer that in more than a few instances the cabri flying of a much used Farman could be traced to the oil- saturated condition of the tail planes. Would it not be a much better plan in such a case to treat the tail fabric so that the oil could be easily removed instead of adopting the usual expedient of increasing its angle of incidence, and so diminishing its efficiency ?
Both the Nieuport and the Deperdussin firms in the manufacture of their machines treat not only the supporting surfaces, but also the covered-in fuselages, with a preparation that is marketed in France under the style of “Emaillite,” which is in effect similar to the Morane composition, with the exception that instead of being colourless it is of a brownish tint.